In printing devices such as a thermal printer, there is known a printing device incorporating a head-pressing mechanism that causes a printhead having lined heat elements to abut on a paper sheet conveyed in a predetermined direction by pressing the printhead in a direction orthogonal to the paper-conveyance direction. This type of printer is typically provided with a printhead mechanism having a supporting mechanism supporting the printhead so as to slidably move in the head-pressing direction to maintain an appropriate print pressure to the paper. In such printers and mechanisms, a rotational moment is produced in a pressing part by virtue of a frictional force caused between the printhead, and a paper sheet or ink ribbon.